"There's only one way to lose this election -- if you fold your hands and don't vote," Obama said

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Getting into the Las Vegas spirit, President Barack Obama told Nevadans late Sunday they have a winning hand in Democrats Hillary Clinton and Senate candidate Catherine Cortez Masto.

Obama was campaigning to boost Clinton's prospects and help Democrats to retake Senate control, scheduling a stop Sunday in tightly contested Nevada before headlining party fundraisers in California.

"You've got black jack," Obama told a crowd of 3,000 boisterous supporters packed into a local high school, while another 2,100 were in an exterior courtyard.

Obama was unsparing in his criticism of Trump, describing the billionaire businessman as unfit to serve as president. Obama said that for years, Republican politicians and far right media outlets have trumped up "all kinds of crazy stuff" about him, Clinton and Reid. He cited as an example those who questioned whether he was born in the U.S. or alleged that he would take everybody's guns away.

"Is it any wonder that they ended up nominating somebody like Donald Trump," Obama said, claiming that Republican lawmakers stood by and said nothing because it gave them a political advantage.

"So Donald Trump did not start this," Obama said. "He just did what he always did, which is slap his name on it, take credit for it and promote it."

But Obama also tried to make life difficult for Republican candidates who have recently sought to distance themselves from the GOP nominee, and on Sunday, it was Rep. Joe Heck's turn.

Heck and Cortez Masto are vying to replace Sen. Harry Reid, the leading Democrat in the Senate who is retiring after serving out his fifth term. Obama said Cortez Masto would be the first Latina to serve in the U.S. Senate and believes that every family should have the chance to pursue the American dream. He said that Trump had once referred to some immigrants from Mexico, where Cortez Masto's grandfather was from, as criminals or rapists.

After a 2005 video emerged of Trump making vulgar remarks about women, Heck said he couldn't support Trump. But Obama said GOP candidates were simply reacting to Trump's slipping poll numbers.

Polls indicate that the presidential and Senate races in Nevada are extremely tight. Reid's seat is considered the only one Republicans could reasonably flip to their side this election. Outside groups have spent tens of millions of dollars trying to influence the outcome.

Obama's standing in the polls has made him a popular surrogate for congressional candidates hoping that a decisive Clinton victory will benefit them as well. The White House has said that Obama's primary mission in the next two weeks will be helping Clinton, but he will also use his appearances at campaign events and in television ads to support Democratic candidates up and down the ballot, even in some state legislative races.

Heck was one of the first GOP candidates to withdraw his backing from Trump. Heck's decision could help him appeal to moderate voters, but he risks alienating some of Trump's ardent supporters.